<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>欢迎注册</title>
    <link href="css/register.css" rel="stylesheet">
</head>
<body>

<div class="form-div">
    <div class="reg-content">
        <h1>欢迎注册</h1>
        <span>已有帐号？</span> <a href="login.html">登录</a>
    </div>
    <form id="reg-form" action="#" method="get">

        <table>

            <tr>
                <td>用户名</td>
                <td class="inputs">
                    <input name="username" type="text" id="username">
                    <br>
                    <span id="username_err" class="err_msg" style="display: none">用户名己存在～</span>
                </td>

            </tr>

            <tr>
                <td>密码</td>
                <td class="inputs">
                    <input name="password" type="password" id="password">
                    <br>
                    <span id="password_err" class="err_msg" style="display: none">密码格式有误</span>
                </td>
            </tr>


            <tr>
                <td>验证码</td>
                <td class="inputs">
                    <input name="checkCode" type="text" id="checkCode">
                    <img src="imgs/a.jpg">
                    <a href="#" id="changeImg">看不清？</a>
                </td>
            </tr>

        </table>

        <div class="buttons">
            <input value="注 册" type="submit" id="reg_btn">
        </div>
<!--        <div class="buttons">-->
<!--            <input type="button" value="发送异常请求" id="btn" />-->
<!--        </div>-->
        <br class="clear">
    </form>

</div>
<script>
    // 1. 给用户名输入框绑定：失去焦点
    document.getElementById("username").onblur = function () {
        // 2. 发送ajax请求
        // 获取用户名的值
        var username = this.value;
        
        // 2.1. 创建核心对象
        var xhttp;
        if (window.XMLHttpRequest) {
            xhttp = new XMLHttpRequest();
        } else {
            // code for IE6, IE5
            xhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
    
        // 2.2. 发送请求
        xhttp.open("GET", "http://localhost:8080/ajax-demo/selectUserServlet?username=" + username);
        xhttp.send();
    
        // 2.3. 获取响应
        xhttp.onreadystatechange = function() {
            if (this.readyState == 4 && this.status == 200) {
                // alert(this.responseText);
                // 判断
                if (this.responseText == "true"){
                    // 用户名存在, 显示提示
                    document.getElementById("username_err").style.display = '';
                }else {
                    // 用户名不存在，清除提示信息
                    document.getElementById("username_err").style.display = 'none';

                }
            }
        }
    }




</script>



<!--<script>-->
<!--    document.getElementById("btn").onclick = function () {-->
<!--        // 1. 创建核心对象-->
<!--        var xhttp;-->
<!--        if (window.XMLHttpRequest) {-->
<!--            xhttp = new XMLHttpRequest();-->
<!--        } else {-->
<!--            // code for IE6, IE5-->
<!--            xhttp = new ActiveXObject("Microsoft.XMLHTTP");-->
<!--        }-->

<!--        // 2. 发送请求-->
<!--        xhttp.open("GET", "/ajax-demo/ajaxServlet");-->
<!--        xhttp.send();-->

<!--        // 3. 获取响应-->
<!--        xhttp.onreadystatechange = function() {-->
<!--            if (this.readyState == 4 && this.status == 200) {-->
<!--                alert(this.responseText);-->
<!--            }-->
<!--        }-->
<!--    }-->
<!--</script>-->
</body>
</html>